DODGE RAM SPARK PROBLEM

1987 Dodge Ram • 89,000 miles

Start the truck and runs but as soon as I let the key off of start it dies. Replaced pickup coil in distributor, ecu thing they had in 80's dodges. Cap and rotar, plugs and plug wires. And can't find the box with the rod from the key that Chevys have? What do I do?

Replace the ballast resistor. You're a youngster, aren't you? That was a real common problem years ago. That resistor is bypassed by the ignition switch in the "crank" position to create a stronger spark. During cranking battery voltage gets drawn down and that voltage feeds the ignition coil. The lower voltage means lower spark voltage and harder starting. Bypassing the resistor gets the voltage back up.

If the pickup coil was defective the engine wouldn't run at all. That system was introduced by Chrysler on Dodges in '72 and Chryslers and Plymouths in '73. It was the industry's first fully electronic ignition system with no breaker points. It's reliable, simple, effective, and easy to diagnose and repair.

Most common cause of backfiring when nothing else has changed is bad spark plug wires or a weak ignition coil. Another possibility is a burned intake valve but that's not common.

If the problem started after parts were replaced look first at the gap for the pickup coil in the distributor. As I recall that should be.012". I had a problem on my '78 LeBaron when I couldn't get the rotor off. I cracked it in two with a hammer and screwdriver. That resulted in a bent shaft and it pushed the pickup away another.006". After I managed to pound the shaft straight again I had a no-start because the gap was.018".

Disconnect and plug the vacuum hose to the distributor. If the backfiring stops, besides the air gap, look for signs of carbon-tracking on the distributor cap. If you have a V-8 engine, look at the four spark plug wires where they're clipped to the rear of the left valve cover. They should not be in the order of the spark plugs, (1, 3, 5, 7). Number 5 should be on one side, then follow the rest in order so it's 5, 1, 3, 7. You want 5 and 7 as far apart as possible. 7 fires right after 5 in the firing order, and under some conditions the spark for cylinder 5 can electromagnetically couple to the wire for cylinder 7 and cause that spark plug to fire as the piston is on its way up on the compression stroke.

If you see a switch with only two wires that is likely for the key-in buzzer.

If the new resistor didn't solve the problem there has to be a broken wire. Turn the ignition switch on to the "run" position, then measure the voltage on both sides of the resistor. There must be 12 volts on one side. The other side may have 12 volts too or a little less but it can't have 0 volts.